Japanese Patent Application Laid-Open No. 2000-296336 describes a method of producing a catalyst for the production of methacrylic acid, which comprises mixing a solution or a slurry containing at least molybdenum, phosphorous and vanadium and a solution or a slurry containing an ammonium compound and to the obtained mixture or mixed slurry, adding a solution or a slurry containing potassium or the like.
However, the catalyst produced by the method described in this publication has an insufficient yield of methacrylic acid in some cases and an improved catalytic performance as an industrial catalyst is in demand.